1904: Mark Hanna (R) vs. Alton Parker (D) vs. Theodore Roosevelt (P)

[President Johnson]

Summer 1904: Senator Mark Hanna, a conservatve who backed McKinley the previous elections, takes the Republican nomination away from incumbent President Theodore Roosevelt, who became president after McKinley's death in 1901. He regards Teddy as too progressive. While the Democrats nominate Alton B. Parker, TR decides to run as a progressive candidate on a third party ticket. What happens?

(The 1904 GOP nomination was uncontested IRL; because Hanna died in early 1904)

[TaylorFillmore]

The 1904 is a great upset in favour of Alton Parker and his running mate Adlai Stevenson. The progressive faction of the Republican Party is very strong and although many stay loyal and Support Hanna the majority back Roosevelt. Alton Parker runs a smooth campaign and issues of Mark Hanna's health plague his campaign. The election comes down to New York where Teddy Roosevelt plays the spoiler in his home state giving the state and election to Alton Parker.

Judge Alton Parker (D-New York) / Former Vice President Adlai Stevenson (D- Illlinois) - 249 EV
Senator Mark Hanna (R- Ohio)/ Senator Charles Fairbanks (R- Indiana) -227 EV

[TaylorFillmore]

Don't know why Florida was in the Republican column.

New Results
Parker/Stevenson -254 EV
Hanna/ Fairbanks -222 EV
New York is still the balance of the election

[🐒Gods of Prosperity🔱🐲💸]

Sen. Hanna is an able campaigner and respected politician running on a message of cooperation between business, labor, and farmer.   Nonetheless, the 3rd party candidacy of the energetic President Roosevelt manages to split the GOP in half, as many remain loyal to the incumbent, especially out West where his Square Deal platform is popular.  As a result, Judge Alton Parker ekes out a narrow electoral majority.

Judge Alton Parker (NY) /  Henry G. Davis (WV) 239 35.4%
President Teddy Roosevelt (NY) / Gov. Albert Cummins (IA) 109  30.1%
Sen. Mark Hanna (OH) / Rep. Robert Hitt (IL) 128  29.2%
Other 5.3%

[Sir Mohamed]

Sen. Hanna is an able campaigner and respected politician running on a message of cooperation between business, labor, and farmer.   Nonetheless, the 3rd party candidacy of the energetic President Roosevelt manages to split the GOP in half, as many remain loyal to the incumbent, especially out West where his Square Deal platform is popular.  As a result, Judge Alton Parker ekes out a narrow electoral majority.

Judge Alton Parker (NY) /  Henry G. Davis (WV) 239 35.4%
President Teddy Roosevelt (NY) / Gov. Albert Cummins (IA) 109  30.1%
Sen. Mark Hanna (OH) / Rep. Robert Hitt (IL) 128  29.2%
Other 5.3%

That looks realistic. Probably you can flip NH and IL. That would give Parker a larger electoral college majority.